This proposal requests $300,000 towards the purchase of a VG70- 250SE mass spectrometer to replace a 10 year old Kratos MS25S. The shared instrument will be housed in the new mass spectrometry laboratory at the Laurel Heights Campus of the University of California, San Francisco. Professor George Kenyon, Chairman of the Department of Pharmaceutical Chemistry at U.C.S.F. and a frequent user of mass spectrometry, will serve as Principal Investigator and Chairman of the Advisory Committee. Dr. Arnold Falick, the Deputy Director of the Biomedical Research Resource Mass Spectrometry Facility, will be in charge of the day to day supervision of the instrument. The major user group consists of eleven investigators with NIH sponsored research interests. Proposals focus on the structural analysis of complex carbohydrate systems of biological importance and the synthesis, metabolism, and toxicity of various xenobiotics. The principal justification for the requested instrument is the need to establish a state of the art capability in capillary column gas chromatography/mass spectrometry, with emphasis on high resolution chemical ionization. Problem solving applications will provide critical structural information on molecules present in complex mixtures at a very low concentration. An Advisory Committee will be responsible for the overall guidance of the shared instrumentation program and for the resolution of scheduling problems. Up to 25% of instrument time will be available for samples originating outside the principal user group. Membership in the principal user group can be achieved following approval of the principal investigator with review by the Advisory Committee. The University has committed over $100,000 towards the purchase of the instrument and for a full service contract. Long range maintenance and upkeep responsibilities will be funded through a combination of University and user support funds.